The use of aluminum and aluminum alloys in the manufacture of vehicle bodies and other automotive parts is of increasing interest nowadays as manufactures and regulators strive to reduce fuel consumption and air pollution. This has lead to the use of adhesives for bonding aluminum parts since welding of aluminum is problematic and inefficient. However, conventional lubricants used for coating sheet surfaces during sheet manufacture tend not to be compatible with the adhesives suitable for the bonding process and new lubricants have been developed to overcome this problem. These new lubricants usually have the properties of waxes, i.e. they are solid at room temperature but melt to low viscosity liquids (e.g. liquids of viscosity less than 50 centipoise, and often less than 30 centipoise) at slightly higher temperatures (e.g. 30 to 100.degree. C., or more commonly 30-50.degree. C., depending on the identity and formulation of the lubricant).
At present, a heated roller coater is normally used to apply such lubricants, but inefficiencies are encountered because the distribution of the coating material across the strip surface becomes variable due to the tendency of the low viscosity lubricant to flow in irregular patterns over the metal surface following its initial application.
Moreover, sufficient heat is transferred to the metal sheet by the coater during the coating process that solidification of the lubricant is delayed. Unless. special precautions are taken, e.g. the installation of a separate cooling zone downstream of the coater apparatus, the lubricant may still be in a molten state when the sheet reaches the coiler apparatus provided for coiling the strip article after coating. If the lubricant is still molten while the strip is being coiled, the coiling pressure exerted on the strip surface will cause unacceptable thinning of the lubricant film, with excess material being forced out through the sides of the coil. Additionally, the very low strip surface friction can cause the coil to become unstable and to "telescope" during the coiling operation.
There is accordingly a need for an improved method of coating metal sheet with wax-like materials of this kind.